Tunable, rapid uptake, aminopolymer aerogel sorbent for direct air capture of co2

ABSTRACT

A method of fabrication of a porous polymer aerogel amine material includes preparing a solution comprising at least a solvent, amine monomers having protecting groups, one or more crosslinkers, and one or more radical initiators, heating the solution to promote polymerization and to produce a polymerized material, performing solvent exchange with the polymerized material, causing a deprotection reaction in the polymerized material to remove the protecting groups to produce a deprotected material, soaking and rinsing the deprotected material to remove excess reagents and any byproducts of the deprotection reaction, and drying the deprotecting material to produce the amine sorbent. A system to separate CO 2  from other gases has a polymer porous aerogel sorbent having greater than 5 wt % of amine containing vinyl monomers integrated into a polymer backbone, and the amine containing vinyl monomers may have a molecular weight of less than 100 g/mol.

RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional applicationSer. No. 17/211,588, filed Mar. 24, 2021, which claims priority to andthe benefit of U.S. Provisional Application No. 63/031,098 filed May 28,2020, which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

This disclosure relates to capture of carbon dioxide, more particularlyto direct air capture using solid sorbents.

BACKGROUND

In the coming decades, integrated assessment modeling predicts thatnegative CO₂ emissions could be required on the scale of ˜10 Gigatons(Gt) of CO₂ per year to reach the International Panel on Climate Changetarget for 2° C. global warming. If deployed in concert withdecarbonization activities and inexpensive, natural negative emissionsapproaches, direct air capture of CO₂ (DAC) is a promising strategy forclimate change mitigation due to its low land use footprint, flexiblerequirements for plant siting, and compatibility with high-capacitygeologic sequestration reservoirs.

However, cost and energy of CO₂ capture in DAC is high, with costestimates ranging from $100-1000/ton-CO₂, and energy estimates of 4-13GigaJoules/ton-CO₂. Compared to DAC processes that use liquid alkalisorbents, DAC processes with solid sorbents have greater potential toreduce cost and energy consumption because of their simpler processflows, faster CO₂ uptake, elimination of evaporative heat loss, lowersensible heat load in regeneration, and lower regeneration temperaturesof less than 200° C. instead of greater than 700° C. Compared to DAC orother CO₂ capture processes with liquid amines, solid sorbents are morechemically stable and release fewer volatiles.

However, to bring down the cost and energy consumption of DAC,significant advances in solid sorbent materials are needed. Inparticular, the National Academy of Sciences (NAS) recently identifiedthe need to develop sorbent materials with (1) increased CO₂ capacity,(2) faster diffusion kinetics, (3) longer cycle lifetime, (4) cost below$50/kg, and (5) minimized sensible heat load from inert supports.

SUMMARY

According to aspects illustrated here, there is provided a method offabrication of a porous polymer aerogel amine material that includespreparing a solution comprising at least a solvent, amine monomershaving protecting groups, one or more crosslinkers, and one or moreradical initiators, heating the solution to promote polymerization andto produce a polymerized material, performing solvent exchange with thepolymerized material, causing a deprotection reaction in the polymerizedmaterial to remove the protecting groups to produce a deprotectedmaterial, soaking and rinsing the deprotected material to remove excessreagents and any byproducts of the deprotection reaction, and drying thedeprotecting material to produce the amine sorbent.

According to aspects illustrated here, there is provided a system toseparate CO₂ from other gases having a polymer porous aerogel sorbenthaving greater than 5 wt % of amine containing vinyl monomers integratedinto a polymer backbone.

According to aspects illustrated here, there is provided A system toseparate CO₂ from other gases having a polymer porous aerogel sorbenthaving greater than 5 wt % of amine containing vinyl monomers covalentlyintegrated into a polymer backbone, wherein the amine containing vinylmonomers have a molecular weight of less than 100 g/mol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a solid sorbent according to the presentembodiments.

FIG. 2 shows a flow chart of an embodiment of a process to manufacture ahigh amine loading sorbent.

FIG. 3 shows a comparison of polymers from conventional radicalpolymerization and from controlled radical polymerization.

FIG. 4 shows an embodiment of a process of fabricating high amineloading sorbent.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments here involve a solid sorbent and process for itsfabrication that will deliver simultaneous advances in all areasidentified by the National Academy of Sciences (NAS), with the potentialto achieve a disruptive process cost below $100/ton-CO₂.

Due to the low content of CO₂ in air, approximately 400 ppm, in DAC,materials with high selectivity chemical sorption are required. Due tohigh CO₂-selectivity, moisture-tolerance, high heat of adsorption, andlow cost, solid amine-modified materials are the most promising solidsorbent materials for DAC. A wide range of amine-modified sorbents havebeen reported but process costs remain high due to materials and processlimitations. For example, one approach uses a solid amine sorbent andreports a cost of $600/ton-CO₂. Other materials such as MOFs and porouspolymer networks (PPNs), which are amorphous hypercrosslinked networksof rigid, tetrahedral monomers, have been proposed, but these sufferfrom high cost, degradation in moisture, and slow uptake rates due tosmall pore size.

The embodiments here involved the use of aminopolymers aerogel sorbentsfor direct air capture of CO₂. The embodiments of TRAPS are shown incomparison with state of the art (SOA) sorbents (Table 1).

TABLE 1 Aminopolymer aerogel properties vs. state-of-the-art sorbents,in DAC conditions. Porous PEI/ Amine-grafted Polymer Material SilicaSilica MOFs Networks Embodiments Equilibrium CO₂ loading   2-2.5 1-2  1-3.9 <1 >1, >3, >4 [mmol/g] CO₂ uptake kinetics 0.007 0.01-0.05 0.01No data, 0.15 [mmol/g/min] ~MOF Cost [$/kg] 25 <50  50-100  100-1000 5-17 Degradation 0.5-7   <2 1 High <0.05 (% capacity fade/cycle)Minimum sensible heat 40 80 30 No data 26 [kJ/mol-CO₂] Specific surfacearea [m²/g] <100 100-400 1000 500-730 >500 Pore size [nm] N/A <10 <1 1-100 10-30

In general, low-cost sorbents such as amine-grafted or amine-impregnatedsilicas have low capacities, high sensible heat loads, and high. Incontrast, high-capacity sorbents such as metal organic frameworks (MOFs)or porous polymer networks have the disadvantage of high cost. The term“sensible heat load” refers to the amount of energy needed to increaseor decrease the temperature of a substance.

The embodiments here involve a novel material comprised of a scalablemesoporous polyamine aerogel with high accessible surface area and highcontent of backbone-integrated amine groups for selective CO₂ sorptionin Direct Air Capture (DAC) conditions. The embodiments also include anovel process for direct incorporation of low molecular weight aminessuch as vinyl amine and allyl amine, while not being restricted to onlyprimary amines, from amino-vinyl monomers by controlled radicalpolymerization process. This achieves high content of aminefunctionalities in the sorbent, which enables high CO₂ loading capacity.

The embodiments here will have higher specific surface area atcomparable pore-sizes in the range of 10-1000 nm than amine-graftedmesoporous silicas, or amines blended with porous ceramic supports suchas blends of polyethyleneimine. This increases gas-sorbent interactionand results in faster loading/unloading rates.

Due to the use of starting materials with highly active primary aminesand avoidance of inert support, the embodiments will have higherequilibrium specific capacity than conventional unsupported as well asceramic-supported polyamines.

The tunability of the synthesis platform of the embodiments enablescovalent integration of amines into the polymer backbone and precisecontrol of the steric environment to achieve longer lifetimes thanconventional polyamines.

FIG. 1 shows a diagram representing the resulting solid sorbent 10 ofthe embodiments. The polyamines 16 are integrated into the polymerbackbone in high content enabling high amine content overall, in thesorbent. In one example, an aerogel is the result of copolymerization ofa mixture containing 90 wt % vinyl amines, which is the smallest vinylamine analog, and 10 wt % crosslinker, the content of nitrogen atom inthe aerogel is 29.3 wt %. An aerogel made entirely of vinyl aminewithout any crosslinker, would have a content of nitrogen atom equal to32.55 wt %. In practice, the percentage of nitrogen in aerogels suitablefor the purpose of this application may range from 1 wt % to 33 wt %.This high content of polyamines, together with the small pore walls, asan example 10 nm, give the polymer backbone a high CO₂ loading capacityin the range of 4 mol CO₂/kg, over 1 mol CO₂/kg or 1-4 mol CO₂/kg, or1-5 mol CO₂/kg. The embodiment may be an aerogel that has a loadingcapacity over 1 mmol CO₂/g of sorbent at temperatures greater than 0° C.and CO₂ concentration of less than 1000 ppm.

The embodiments include an aerogel having uptake kinetics of greaterthan 0.05 mol CO₂ per kilogram minute, including at temperatures greaterthan 0° C. and CO₂ concentration of less than 1000 ppm. In oneembodiment, the resulting aerogel has greater than 5 wt % of aminecontaining vinyl monomers integrated into a polymer backbone.

The backbone polymer has cross-linkers such as 14, but of lower content,allowing mechanical robustness and low sensible heat load to the sorbentwhile further contributing to increased capture of CO₂ 18. The sorbenthas fast kinetics, in the range of 0.15 mol CO₂/kg·min, is mesoporouswith pore size in the range of 10-30 nm as an example, and has aspecific area of over 500 m²/g. The sorbent kinetics can also be in therange of 0.01-0.5 mol CO₂/kg·min, 0.05-0.5 or any subset of thoseranges. The pore sizes of the sorbent can also range from 1-50 nm, 1-100nm, 1-200 nm, or 1-500 nm, or subsets and combinations of those ranges.The sorbent can also have specific surface area of greater than 100m²/g, 200 m²/g, 300 m²/g, 400 m²/g, 600 m²./g, 700 m²/g, 800 m²/g, 900m²/g, 1000 m²/g, 1100 m²/g, and 1200 m²/g.

One embodiment is a process for fabrication of porous polymer aerogelswith high content backbone-integrated amine groups and with small sizepores and thin pore polymer walls. FIG. 2 shows an embodiment of aprocess. One should note that no order of the subprocesses is implied,nor should any be inferred. The process involves preparation of asolution at 20 that includes a solvent, low molecular weight vinyl aminemonomers, one or more crosslinkers comprising two or more vinyl groups,one or more radical initiators, a nitroxide mediator, and possibly oneor more reducing agents, although these are optional. The low molecularweight vinyl amine monomers may have the amine group protected toprevent its reaction with other vinyl reagents including thecrosslinkers and vinyl amine themselves.

Low molecular weight means having molecular weight below 100 g/mol,below 300 g/mol, below 1000 g/mol, or below 5000 g/mol. A vinyl amine isa molecule that contains a vinyl functional group or a functional groupthat contains a vinyl group such as an acrylate or methacrylate, and anamine group (primary, secondary, or tertiary), RNH₂, R₂NH, or R₃N. Theamine in vinyl amine can also refer to functional groups that can beconverted to amines such as amides, formamide, and others. The vinylgroup and amine group may be bonded directly to each other, or may haveother atoms or subgroups between them, such as 0-6 carbon atoms.

The process then removes oxygen from the above solution and heats theresulting solution at 22 to promote polymerization to produce apolymerized material. The process performs a solvent exchange at 24 withan appropriate solvent such as water or water mixtures withwater-soluble organic solvents, polar solvents, mixtures of solventscontaining a polar solvent, protic solvents or mixtures of solventscontaining protic solvents. A deprotection reaction removes the amineprotecting groups and the process rinses the material at 26. The solventexchange and deprotection reaction may take place in either order.Soaking and rinsing the resulting material with water, water mixtureshaving water miscible organic solvents, polar solvents, mixtures ofsolvents containing a polar solvent, protic solvents, or mixtures ofsolvents containing protic solvents removes excess reagents and solubledeprotection reaction byproducts. Finally, drying produces the finalamine sorbent at 28.

The embodiments have several unique features. These include developmentof polymer porous structures by direct incorporation of low molecularweight vinyl amine monomers by controlled radical polymerization, stablefree radical polymerization (SFRP). They also include development of asynthetic process for co-polymerization of amine-containing vinylmonomers with vinyl crosslinkers, producing porous polymers with smallpore size in the range of 10 nm-1000 nm, and thin walls in the range of10-100 nm, and with high amine groups content of greater than 10 wt % ofincorporated amine containing vinyl monomer integrated into the polymerbackbone. Polymerization or co-polymerization of primary and secondaryamine-containing vinyl monomers is not possible due to the reaction ofthe amine groups with vinyl groups present in the amine-containing vinylmonomers of the crosslinkers.

The process can be used to tune the diameter of the pore wallstructures, ensuring full utilization of the polyamine and rapid uptake.With thicker pore walls found in prior art solid sorbents a largefraction of the amines is incorporated into the dense pore polymer walland are kinetically unavailable for CO₂ capture. Thin polymer wallshaving thickness in the range of 10-100 nm, (or 1-100 nm, 1-500 nm, or10-500 nm) achieved with the embodiments have two benefits, a highersurface area to volume ratio, and shorter diffusion time for gas topenetrate the solid material, and as a result, more of the amino groupsare available for interaction with gas for CO₂ capture. The net effectis an increased CO₂ capture capability when compared with currentapproaches.

Other unique aspects include high amine loading which provides increasedCO₂ equilibrium loading capacity under DAC ambient conditions.Particularly beneficial are primary amine groups chemically optimizedfor low-CO₂ partial pressure adsorption. They also include increasedmechanical and physical stability of sorbent particles made from thisporous sorbent material, measured by increased crush strengthresistance, and decreased attrition index, which make particles madewith the disclosed amine sorbent suitable for CO₂ capture by fluidizedbed processes. The embodiments have improved stability against thermaland oxidative degradation when compared with other sorbents such assilica grafted with longer amine chains and other solid or liquid aminesorbents. This improved stability results from the steric effect of thepolymer backbone that is in very close proximity to the amine groups andby elimination of metals that catalyze degradation.

The SFRP (stable free radical polymerization) aerogel process has beendemonstrated in a variety of non-amine monomers, such as those disclosedin US Patent Publication No. 2020/0031977, and U.S. Pat. No. 10,421,253incorporated by reference herein in their entirety. As shown in FIG. 3 ,in conventional radical polymerization, various polymer chain ends 30grow at different rates and can terminate through chain-chaintermination events by coupling of the radicals 32 at the end of thechain, producing an inactive polymer chain 34 which stops growing. Thefinal result is a porous sorbent structure made of large aggregateparticles 36 that has moderate specific surface area and large porewalls.

The SFRP unique aerogel process, like those processes patented by PARC(Palo Alto Research Center, Inc.) modulates chain growth andprecipitation of nanogel clusters during polymerization as shown in thebottom of the diagram. In SFRP, a nitroxide mediator 44 reversibly bindsto the ends 42 of growing chains 40, producing a ‘dormant’ state. Chaingrowth occurs only when the nitroxide mediator 44, such as TEMPO-OH,decouples from the chain end and allows a new monomer molecule 46 toreact with the growing chain. As chains spend most of the time in thedormant state, the reaction proceeds as a living polymerization withlowered probability of undesirable chain termination events. The endresult is a high porosity polymer structure 48 with high specificsurface area and thin walls. SFRP decreases the pore wall size andincreases the surface area at equivalent porosity.

Previous work shows that polymerization or co-polymerization of primaryand secondary amine-containing vinyl monomers is not possible due to thereaction of the amine groups with vinyl groups present in theamine-containing vinyl monomers of the crosslinkers (Tillet, G.,Boutevin, B. & Ameduri, B. Chemical reactions of polymer crosslinkingand post-crosslinking at room and medium temperature. Prog. Polym. Sci.36, 191-217 (2011)). The processes of these embodiment utilizes vinylamine monomers wherein the amine groups are protected during thepolymerization step. The protecting groups are removed afterpolymerization to produce the porous polymer aerogels with a highcontent of backbone-integrated amine groups, which are enabled tocapture CO₂. Any process for protecting/deprotecting the amine groups issuitable for the purpose of the embodiments. In some cases, secondaryand tertiary amines do not require protecting groups. In secondary andtertiary amines, a nitrogen atom is bonded to one or zero hydrogens andtwo or three non-hydrogen atoms or chemical groups. In cases where aprotecting group is not needed, one or two of the non-hydrogen groupsprevent side reactions during polymerization.

One process for protection/deprotection of primary and secondary aminecontaining vinyl monomers has been described previously athttp://cssp.chemspider.com/article.aspx?id=103. Protection by reactionwith formamide typically involves reacting the amine with formic acid inacetic anhydride while heating typically at 50-80° C., followed bysolvent evaporation and purification by chromatography.

FIG. 4 illustrates an embodiment of a synthetic process. Vinyl monomerswith protected amines are suitable because they can be efficientlypolymerized by conventional (uncontrolled) radical polymerizationprocess. N-vinylformamide (1), wherein the amine is protected byformaldehyde at 50 is an example suitable for the present embodiments(Zhu, J., Gosen, C. & Marchant, E. R. Synthesis and Characterization ofPoly(vinyl amine)-Based Amphiphilic Comb-Like Dextran Glycopolymers by aTwo-Step Method. J Polym Sci Part A Polym Chem 44, 192-202 (2006)). Inthe first step, a solvated gel is fabricated by copolymerization of theN-vinylformamide with multifunctional crosslinker such as for exampledivinylbenzene (DVB, trimethylolpropane trimethacrylate, 1,6-hexanedioldiacrylate, multifunctional acrylates, or multifunctional methacrylates)in SFRP conditions (100-130° C., 6-48 hr), initiated by an initiatorsuch as benzoyl peroxide, lauroyl peroxide, or AIBN and by using anitroxide mediated chain growth additive (TEMPO, TIPNO, SG1, TEMPO-OH)in a suitable solvent as a porogen. To achieve porosity of greater than30%, solvent concentrations ranging from 50-80 wt % of the overallsolution may be used. In general, solvent concentrations 20-90 wt % or20-99 wt % may be used. In the second step, the amine is regenerated byremoving the formyl group under acidic and basic conditions, andoptionally with ion exchange resins, as reported in prior art (Wang, andMohammadi, Z., Cole, A. & Berkland, C. J. In situ synthesis of ironoxide within Polyvinylamine nanoparticle reactors. J. Phys. Chem. C 113,7652-7658 (2009)). Finally, the solvated gel is dried under controlledambient conditions, by protocols developed previously by PARC fornon-amino aerogels.

Low molecular weight vinyl amines are preferred to increase the contentof nitrogen atoms required for CO₂ capture. In the porous amine aerogel,the amine groups resulted from the polymerization of the amine vinylmonomers may connect to the polymer backbone by hydrocarbon chainconsisting of 0 to 6 carbon atoms. As an example, if the vinyl aminemonomer is vinyl amine, the number of carbon atoms in the connectinghydrocarbon chain is 0. If the vinyl amine monomer is 3-buten-1-amine,the number of carbon atoms in the connecting hydrocarbon chain is 2.

Suitable low molecular weight amines substituted vinyl monomers whichare to be used as protected amines, for the present embodiments include:amine monomers having protected amine groups, low molecular primaryamines including vinyl or amine monomers, i.e. containing polymerizabledouble bonds, include vinyl amine, allyl amine, 3-buten amine,4-pentene-1-amine, 3-vinylaniline, 4-vinylaniline, diamine vinylmonomers including 4-cyclohexene-1,2-diamine and the like. Also, aminecontaining acrylates and methacrylates are suitable for theseembodiments, such as for example 2-aminoethyl methacrylate,3-aminopropyl methacrylate.

Also, low molecular secondary amines are suitable for these embodiments.This include N-methylvinyl amine, N-ethyl vinyl amine, N-methyl-allylamine, N-isopropylvinyl amine, N-tert-butylvinyl amine and generally anyof the derivatives that are the result of substituting a hydrogen atomfrom a primary amine containing vinyl monomers.

Suitable vinyl crosslinkers include crosslinkers having two or morevinyl groups, vinyl crosslinkers having double bonds polymerizablegroups, —CH═CH₂, —C(R)═CH₂, —C(R₁)═C(R₂)H, —C(R₁)═C(R₂)(R₃),—CH═C(R₁)(R₂), where R, R₁, R₂, R₃ are alkyl groups including methyl,ethyl propyl, isopropyl and the like. The double bond can be connecteddirectly to a phenyl, biphenyl or anthraces radical such an in the caseof divinylbenzene. The double bond may also be connected to an estergroup, such as in the case of acrylates or methacrylates. Suitableexamples of acrylate and methacrylate crosslinkers include tri, tetra,penta or hexa-acrylates and methacrylates such as trimethylolpropanetriacrylate, trimethylolpropane ethoxylate triacrylate,di(trimethylolpropane) tetraacrylate, dipentaerythritolpenta-/hexa-acrylatetrimethacryl adamantane, dipentaerithritol,trimethylolpropane trimethacrylate, divinylbenzene, phenylenedimethacrylate, phenylene diacrylate, and 1,6-hexanediol diacrylate andsimilar.

Suitable solvents which act as porogens include polar aprotic organicsolvents such as dimethylformamide, methyl ethyl ketone,tetrahydrofuran, diglyme (diethylene glycol dimethyl ether),1,2-dimethoxy-ethane, ethyl acetate and others. Particularly suitableare high boiling solvents with a boiling temperature of greater than160° C., greater than 150° C., or above 130° C., such as acetophenone(202° C.), dimethylsulfoxide (DMSO) (189° C.), sulfolane orn-methylpyrrolidone (202° C.). Solvent/monomer interaction strength canbe tuned to affect porosity and pore size. Generally unfavorableinteractions result in larger pore sizes and larger pore wall features.

Suitable radical initiators include thermal initiators—activated byheat—and photoinitiators which are activated by light, typicallyUltraviolet in a range of about 200 nm to 400 nm wavelength.Non-limiting examples of thermal initiators includes (a) peroxides suchas benzoyl peroxide, diacetylperoxide, di t-butylperoxide, lauroylperoxide, dicumyl peroxide; or azo compounds such asAzobisisobutyronitrile (AIBN) and phenylazotriphenylmethane.Non-limiting examples of photoinitiators include benzophenone,anthaquinone, camphorquinone, benzyl, benzoin, and the like.

Suitable nitroxide mediators include nitroxide species derived from thedecomposition of an alkoxyamine, 4-hydroxy-TEMPO, TEMPO, and other TEMPOderivatives, TIPNO and TIPNO derivatives, chlorobenzyl-TIPNO, SG1 andother SG1 derivatives, and a methacrylic acid radical. A portion of astable free radical may remain in the aerogel structure.

Suitable reaction temperature will typically be in a range from 70° C.to 200° C. depending on the initiation temperature of the radicalinitiator and reactivity of the stable free radical.

The concentration of the amine containing vinyl monomers together withcrosslinkers in the solvent is comprised in a range from 1% to 60% wt ofthe overall solution. Generally, the lower the concentration of monomersand crosslinkers the higher the porosity of the sorbent.

After polymerization, the formyl group is typically removed byhydrolysis under basic or acid conditions followed by rinsing andtreatment with ion exchange resins (Wang). In the proposed process fromthis disclosure, removal of the reagents in excess and of solubledeprotection reaction byproducts by soaking and rinsing with water andwith water mixtures having water miscible organic solvents. Suitablewater miscible solvents include alcohols including methanol, ethanol,propanol, isopropanol, and the like, as well as acetone and THF forexample. One or more water miscible solvents can be used. The amount ofwater miscible solvent in the water solution can range from 0.5% to99.5% of the total weight of the solution.

Drying may involve either ambient, freeze-drying, or supercritical CO₂drying. In ambient drying, the gel immersed in a solvent such as alkanesincluding hexane, heptane, or more polar solvents such as acetone,tetrahydrofuran (THF) or alcohols including methanol, ethanol,isopropanol, and the like, is first dried at room temperature andpressure, and then possibly in vacuum. In freeze-drying, first thesorbent is frozen (by decreasing the temperature below the freezingpoint of the solvent) then the solvent is removed by sublimation invacuum. In supercritical CO₂ drying, gels are solvent exchanged withliquid CO₂ and supercritically dried.

To reduce kinetic barriers, the embodiments must exhibit high porosity,high specific surface area, and thin pore walls. The thin pore wallsenable rapid gas diffusion, CO₂ chemisorption, and diffusion into thebulk at 10 nm scale. In some embodiments, porosity is greater than 10%.In other embodiments, porosity is greater than 20%, 30%, 40%, 50%, 60%and 70%. Thermodynamically, a high loading of selective chemisorbingmoieties is needed to capture large amounts of CO₂ at low partialpressures. The embodiment platform provides explicit control over boththe amine loading and sorbent pore characteristics. SFRP aerogel processresults in gels with higher specific surface areas and smaller pore wallthicknesses compared to those synthesized using uncontrolled radicalpolymerization shown in FIG. 3 .

Important reaction parameters can be leveraged to tune these tradeoffs.Nitroxide mediators reversibly cap the ends of polymer chains duringSFRP. However over the course of reaction, excess nitroxide builds dueto chain termination. If excess nitroxide is unchecked, polymerizationarrests. To counteract this effect, reducing agents such as reducingsugars such as glucose, reagents containing hemiacetal groups,hydroxyacetone, or enediol species derived from ketones and aldehydes,such as ketose and aldose sugars, are used to gradually consume thenitroxide and maintain the ratio of nitroxide to living radicals.Initiators with slow decomposition rates are also effective atcounteracting accumulation of excess free nitroxide. By systematicallytuning parameters such as the solvent-monomer interaction strength,radical initiator half-life, and concentrations of solvent, nitroxide,reducing agent, and radical initiators, various pore structures can beobtained from the same set of monomers.

Controlling the steric environment of the amines maximizes stability andamine utilization. It is expected that amines in a more flexible bondingenvironment will adsorb CO₂ more strongly with a higher heat ofadsorption, whereas more steric hindrance will inhibit oxidation. Due tothe tunability of the embodiment platform, variants of vinylamine suchas allylamine or a secondary amine monomer can easily be substituted inthe synthesis to fine-tune the steric environment and flexibility ofamines.

The embodiments here provide control over the pore wall thickness. Thesize of the rough, porous particles that make up the pore walls can betuned in the 10-100 nm range, or 5-200 nm range, 5-500 nm range, 10-1000nanometers by altering the polymerization activity, which is a measureof the influence the nitroxide mediators have on the polymerization.Pore wall particles are permeable to gases and maximize CO₂ capturecapability by enabling interaction with amine groups inside the polymerwall. This is a distinctive advantage of the sorbent from theseembodiments. Based on typical porosities and surface areas, the hardsphere length scale of the pore wall structures is around 10-100 nm.

The embodiments have advantages over liquid amine sorbents used forsorption at flue gas concentrations by greatly decreasing inert,sensible heat load and decreasing chemical degradation. Highly mobileamines optimized for flue gas conditions are more prone to oxidation andside-reactions than solid, immobilized amines.

The sorbent of these embodiments may be deployed in systems having fixedbed, fluidized bed, or monolith-type sorbers. The aerogel synthesisprocess is flexible and can be used to produce aerogels in a variety ofform-factors ranging from 1-100 μm particles to 0.3×10×10 cm³ or largermonoliths. The sorbent can be produced as monoliths, binder-freepellets, binder-containing pellets, particles, fluidizable particles, orparticles cast onto macroporous substrates and other materials.

The embodiments achieve high specific surface areas at moderate, notextremely high porosities. Due to lower porosity, the embodiments willhave higher thermal conductivity than silica aerogels, around 0.14 W/mK,or greater than 0.02, 0.05, 0.07, or 0.1 W/mK, enabling rapid heatexchange.

While smaller size pores are preferred in the range of 10-30 nm, largersize pores are also suitable, such as a range comprised from 10 nm-1000nm, but they may change the surface area of the sorbent. The thinner thepore wall, the better the better the gas diffusion through the pore walland the higher the CO₂ loading capacity. Thicker walls in the range of10-100 nm are also suitable for the embodiments because they may bebeneficial for improving mechanical strength of the sorbent, but theymay decrease the CO₂ capture loading efficiency. A trade-off betweenthese two-performance metrics may be required to achieve optimalmechanical strength and CO₂ loading capacity. The optimal ranges dependon the mode of use of the sorbent.

The embodiments expect a 7× improvement in oxidative-stability overconventional supported polyethyleneimine (PEI) sorbents, due to theprimary amine structure in the aerogel and covalent incorporation ofamines in the backbone. The aerogel may also contain secondary amines.As with other polyamines, in DAC conditions with ambient humidity,oxidative degradation will be dominant. Recently, supportedpolyallylamine (PAA), which contains only primary amines, was shown tooxidize 7× more slowly than polyethyleneimine (PEI), which contains amix of less stable secondary and primary amines (Bali, S., Chen, T. T.,Chaikittisilp, W. & Jones, C. W. Oxidative stability of aminopolymer-alumina hybrid adsorbents for carbon dioxide capture. Energy andFuels 27, 1547-1554 (2013)). Due to structural similarity, theembodiments should have similar oxidation behavior to PAA. Theembodiments will also demonstrate low physical and chemical degradationrates, due to the rigid structure and covalent incorporation of aminesin the polymer backbone. The embodiments have the potential to reach aneconomically viable lifetime of 10,000 cycles to 90% capacitymaintained. The cycle life of the embodiments is estimated byextrapolating from the cycle life of a secondary amine sorbent based onthe expected 7-fold improvement in oxidative stability and a shortercycle time, assuming air is introduced at temperatures below 65° C.

The embodiments enable low minimum sensible heat load of below 50kJ/mol, such as 26 kJ/mol CO₂ per half cycle by high CO₂ uptakecapacity, because of high amine utilization, coupled with low content ofCO₂-inactive co-monomer. The minimum sensible heat load may also be lessthan 10 kJ/mol, 20 kJ/mol, 30 kJ/mol, 40 kJ/mol, and 50 kJ/mol. Thisparameter is critical to energy of CO₂ capture and DAC process operatingexpenditures. The minimum energy requirement is 40-70% lower than thatof conventional supported polyamines (Table 1), and lower than the heatof adsorption, which is in the range of 45-90 kJ/mol CO₂.

Crush strength and Attrition index (AI) values, which indicatecompatibility of the sorbent with fixed and fluidized bed sorbers, areestimated from DOE-funded literature on benzyl amine ion exchange resinsfor flue gas capture (Sjostrom, S. & Senior, C. Pilot testing of CO₂capture from a coal-fired power plant—Part 1: Sorbent characterization.Clean Energy 3, 144-162 (2019)). These have similar chemical structureand porosity to the embodiments (Alesi, W. R. & Kitchin, J. R.Evaluation of a primary amine-functionalized ion-exchange resin for CO 2capture. Ind. Eng. Chem. Res. 51, 6907-6915 (2012)), but the embodimentshave an AI below 0.5, and added benefits of higher CO₂ capacity andcontrolled porosity. These values compare well with the state of the artattrition-resistant fluid cracking catalysts having an AI in the rangeof 0.2-0.5, (Green, A. D. et al. Carbon Dioxide Capture from Flue GasUsing Dry Regenerable Sorbents. DOE Report, DE-FC26-00NT40923 128(2004)), to which new fluidized bed particles are often compared. Forcomparison, for silica/PEI, the AI is greater than 2, (Kim, J. Y. et al.Continuous testing of silica-PEI adsorbents in a lab.-scale twinbubbling fluidized-bed system. Int. J. Greenh. Gas Control 82, 184-191(2019)), for MOFs, the AI is greater than 10 (Luz, I., Soukri, M. &Lail, M. Confining Metal-Organic Framework Nanocrystals withinMesoporous Materials: A General Approach via ‘solid-State’ Synthesis.Chem. Mater. 29, 9628-9638 (2017)). Improved performance of theembodiments is due to intrinsic toughness and plastic deformation ofpolymers.

The sorbent from the embodiments may be used for other applicationsbeyond DAC, including capture of post combustion gases or indoor CO₂removal. In DAC applications, adsorption can occur at ambientconditions. Ambient conditions are ambient humidity (40-70% RH), aircomposition, CO₂ concentration (100-5000 ppm CO₂ in air, 400-500 ppm CO₂in air), temperature (−40 to 50° C., or 20-30° C.), and absolutepressure (0.5-2 bar, or 1 bar). In other applications, adsorption canoccur at a wider range of conditions such as 0.1-50% CO₂, or 1-90% CO₂,3-15% CO₂, or 3-50% CO₂, 0 to 100% RH, 1 mbar to 10 bar pressure, and15-80° C. or 15-50° C. The sorbent may be used in a variety of systemsand configurations to separate CO₂ or other acidic gases from air orother ambient gases.

All features disclosed in the specification, including the claims,abstract, and drawings, and all the steps in any method or processdisclosed, may be combined in any combination, except combinations whereat least some of such features and/or steps are mutually exclusive. Eachfeature disclosed in the specification, including the claims, abstract,and drawings, can be replaced by alternative features serving the same,equivalent, or similar purpose, unless expressly stated otherwise.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the above embodiments.

What is claimed is:
 1. A method of fabrication of a porous polymeraerogel amine material, comprising: preparing a solution comprising atleast a solvent, amine monomers having protecting groups, one or morecrosslinkers, and one or more radical initiators; heating the solutionto promote polymerization and to produce a polymerized material;performing solvent exchange with the polymerized material; causing adeprotection reaction in the polymerized material to remove theprotecting groups to produce a deprotected material; soaking and rinsingthe deprotected material to remove excess reagents and any byproducts ofthe deprotection reaction; and drying the deprotecting material toproduce the amine sorbent.
 2. The method as claimed in claim 1, whereinpreparing a solution comprises preparing a solution that includes one ormore reducing agents.
 3. The method as claimed in claim 1, whereinpreparing the solution comprising at least amine monomers comprisespreparing the solution comprise one or more selected from the groupconsisting of: amine monomers having protected amino groups, lowmolecular weight vinyl amine monomers, vinyl monomers containingpolymerizable double bonds, amine monomers containing polymerizabledouble bonds, vinyl amine, allyl amine, 3-buten-1-amine,4-pentene-1-amine, 3-vinylaniline, 4-vinylaniline, diamine vinylmonomers including 4-cyclohexene-1,2-diamine, amines containingacrylates and methacrylates, 2-aminoethyl methacrylate, and3-aminopropyl methacrylate, N-methylvinyl amine, N-ethyl vinyl amine,N-methyl-allyl amine, N-isopropylvinyl amine, N-tert-butylvinyl amine,and any derivatives thereof that result from substituting a hydrogenatom from a primary amine containing vinyl monomers.
 4. The method asclaimed in claim 1, wherein preparing the solution comprising at leastone or more crosslinkers comprises preparing the solution in which thecrosslinkers comprise one or more selected from the group consisting of:crosslinkers consisting of two or more vinyl groups, vinyl crosslinkersthat include double bond polymerizable groups, —CH═CH₂, —C(R)═CH₂,—C(R₁)═C(R₂)H, —C(R₁)═C(R₂)(R₃), —CH═C(R₁)(R₂), where R, R₁, R₂, R₃ arealkyl groups including methyl, ethyl propyl, isopropyl, tri, tetra,penta or hexa-acrylates and methacrylates, trimethylolpropanetriacrylate, trimethylolpropane ethoxylate triacrylate,di(trimethylolpropane) tetraacrylate, dipentaerythritolpenta-/hexa-acrylatetrimethacryl adamantane, dipentaerithritol,trimethylolpropane trimethacrylate, divinylbenzene, phenylenedimethacrylate, phenylene diacrylate, and 1,6-hexanediol diacrylate. 5.The method as claimed in claim 1, wherein preparing the solutioncomprising at least a solvent comprises preparing the solution in whichthe solvent comprises one or more selected from the group consisting of:a polar aprotic organic solvent, dimethylformamide, methyl ethyl ketone,tetrahydrofuran, diglyme (diethylene glycol dimethyl ether),1,2-dimethoxy-ethane, ethyl acetate, high boiling solvents,acetophenone, dimethylsulfoxide (DMSO), sulfolane andn-methylpyrrolidone.
 6. The method as claimed in claim 1 whereinpreparing the solution comprises at least a solvent comprises preparingthe solution comprising a solvent having a concentration from 20-99 wt %of the overall solution.
 7. The method as claimed in claim 1, whereinpreparing the solution comprising at least a radical initiator comprisespreparing the solution with one or more selected from the groupconsisting of: thermal initiators, photoinitiators, peroxides, benzoylperoxide, diacetylperoxide, di t-butylperoxide, lauroyl peroxide,dicumyl peroxide, azo compounds, Azobisisobutyronitrile (AIBN),phenylazotriphenylmethane, benzophenone, anthaquinone, camphorquinone,benzyl, and benzoin.
 8. The method as claimed in claim 1, whereinpreparing the solution comprises preparing the solution to include anitroxide mediator.
 9. The method as claimed in claim 8, whereinpreparing the solution to include the nitroxide mediator comprisespreparing the solution to include one or more selected from the groupconsisting of: nitroxide species derived from the decomposition of analkoxyamine, 4-hydroxy-TEMPO, TEMPO, TEMPO derivatives, TIPNO, TIPNOderivatives, chlorobenzyl-TIPNO, SG1, SG1 derivatives, and a methacrylicacid radical.
 10. The method as claimed in claim 1, wherein heating thesolution comprises heating the solution to a temperature in the range offrom 70° C. to 200° C., where the temperature depends upon an initiatingtemperature of the radical initiator.
 11. The method as claimed in claim1, wherein drying the material comprises one of: ambient drying of thematerial at room temperature and pressure; ambient drying of thematerial at room temperature and pressure and then in vacuum;freeze-drying the material followed by removal of ice by sublimation ina vacuum; and performing solvent exchange with liquid CO₂ andsupercritically drying the material.
 12. A system to separate CO₂ fromother gases, comprising a polymer porous aerogel sorbent having greaterthan 5 wt % of amine containing vinyl monomers integrated into a polymerbackbone.
 13. The system as claimed in claim 12, wherein the polymeraerogel sorbent is one of binder-free pellets, binder-containingpellets, particles, monoliths, fluidizable particles, and particles castonto other materials.
 14. The system as claimed in claim 12, wherein thepolymer aerogel sorbent is used in a sorber comprising one of a fixedbed, fluidized bed, and a monolith-type sorber.
 15. A system to separateCO₂ from other gases, comprising a polymer porous aerogel sorbent havinggreater than 5 wt % of amine containing vinyl monomers covalentlyintegrated into a polymer backbone, wherein the amine containing vinylmonomers have a molecular weight of less than 100 g/mol.
 16. The systemas claimed in claim 15, wherein the polymer aerogel sorbent is one ofbinder-free pellets, binder-containing pellets, particles, monoliths,fluidizable particles, and particles cast onto other materials.
 17. Thesystem as claimed in claim 15, wherein the polymer aerogel sorbent isused in a sorber comprising one of a fixed bed, fluidized bed, and amonolith-type sorber.